Low oxygen conditions (hypoxia) commonly found in solid tumors are considered a major obstacle for the clinical management of cancer by radiation therapy (radiotherapy, RT). Moreover, cancer patients with significantly hypoxic tumors tend to have a poor prognosis for survival. Given the clinical relevance of hypoxia, a long-time objective of experimental RT research has been to effectively radiosensitize solid tumors by attenuating or exploiting this pathophysiological state. Molecular oxygen (oxygen) is a natural and potent radiosensitizer; thus, one strategy for effectively treating hypoxic tumors by RT is to artificially increase their oxygenation. This project aims to use a novel oxygen-delivery technology developed at the University of California, Berkeley (UC Berkeley)-heme-nitric oxide/oxygen-binding (H-NOX) proteins-to revolutionize RT for cancer patients. The H-NOX technology embodies 4 major improvements over prior efforts in the field of oxygen delivery therapeutics: (1) oxygen-binding H-NOXs are neutral towards nitric oxide (NO), comparing favorably with the high NO reactivity and hypertensive properties of cell-free hemoglobin; (2) over 50 H-NOX candidates have been engineered, each with a specific oxygen affinity; the entire panel of vehicles demonstrate oxygen affinities across a 10-million fold range; (3) H-NOX vehicles are structurally stable above 80 0C, and chemically stable for weeks at room temperature; (4) H-NOX vehicles are modular, and can be surface-modified to alter size, oncotic properties, or tissue targeting. In short, the H-NOX technology provides a toolbox of oxygen delivery candidates to test in hypoxic tissues and tumors for their capacity to raise oxygen levels and enhance RT and chemotherapy. Phase I studies successfully identified a lead candidate that penetrates deep into tumors and raises oxygen levels in hypoxic zones. Phase II studies will focus on determining the degree of RT enhancement by lead H-NOX candidates, and refining them for optimal biodistribution, tumor oxygenation, RT enhancement and safety. A lead H-NOX candidate that meets this profile will be eligible for IND-enabling studies in preparation for clinical trials. This Phase II proposal has been prepared in accordance with guidelines for developing radiation enhancement therapies as published by the NCI's Radiation Modifier Working Group. The Phase II milestones have also been discussed with potential corporate partners and venture investors. Successful completion of this study is expected to result in significant investor interest in supporting IND-enabling development for clinical trials. PUBLIC HEALTH RELEVANCE: Low oxygen conditions (hypoxia) commonly found in solid tumors are considered a major obstacle for the clinical management of cancer by radiation therapy (radiotherapy, RT). For the 500,000 cancer patients treated with RT each year, more than 50% present with hypoxic tumors and receive minimal benefit from RT. This project aims to use a breakthrough, oxygen-delivery technology that is tunable, stable, and modular, to revolutionize RT for cancer patients.